arXiv subjects

F. B. M. dos Santos

Publications and source records attributed to F. B. M. dos Santos.

11 recordsLinked to original sources

arXiv2026

ACT DR6+Planck impact on inflation with non-zero vacuum expectation value and the post-inflationary behavior

The impact of the most recent cosmic microwave background (CMB) data from the Atacama Cosmology Telescope (ACT) is studied for a model of cosmic inflation which predicts a non-zero vacuum expectation value (VEV) $M$ for a large-field regime. Since lower values of $M$ are compatible with the higher spectral index $n_s$ provided by the ACT+Planck joint analysis, we establish new limits on this parameter while also considering further CMB data from the latest BICEP/Keck Array release for CMB polarization modes. We find $\log_{10}M/M_{Pl}=-2.5^{+1.1}_{-1.3}$ at 68\% confidence level, compatible with $M/M_{Pl}\simeq 0.003$, which is interesting for post-inflationary processes, such as preheating. We conduct a lattice simulation for the inflaton field for the first few e-folds, as the model is compatible with the production of relics such as oscillons, which are possible candidates as sources of gravitational waves and primordial black holes. We find that the model indeed produces localized, quasi-spherical structures compatible with oscillons, which might lead to signatures detectable by future experiments. However, in agreement with recent works, we find that although the abundance of gravitational waves that could be generated in this regime has an amplitude well within the sensitivities of these detectors, the frequency range is on the GHz limit, away from the expected frequencies. Finally, we estimate the impact of a coupling of the type $yϕχ^2$ to the inflaton, in the realization of perturbative reheating, directly impacting the predictions of the model, as lower values of $M$ are consistent with both the entire allowed temperature range, and the limits imposed by BICEP/Keck Array+Planck+ACT.

astro-ph.CO↗

arXiv2025

Forecasting constraints on quintessential inflation from future generation of galaxy and CMB surveys

We investigate the constraining power of future CMB and galaxy surveys on models of quintessential inflation realized within the framework of $α$-attractors. We analyze how these future datasets will probe the parameter space of $α$-attractor quintessential inflation, specifically the inflationary potential parameters. Our results demonstrate that the synergy between CMB-S4, LiteBIRD, and Euclid can significantly tighten the bounds on the model parameters, achieving forecasted $1σ$ uncertainties of $α=2\pm 0.17$, $n_s=0.965\pm 0.0014$, $\ln(10^{10}A_s)=3.0447\pm 0.0029$ for the CMB+GC$_{sp}$ case. This level of sensitivity will enable us to discriminate between different realizations of quintessential inflation and test the attractor behavior characteristic of these models.

astro-ph.CO↗

arXiv2025

Stage IV CMB forecasts for warm inflation

We report forecast constraints on warm inflation in the light of future cosmic microwave background (CMB) surveys, with data expected to be available in the coming decade. These observations could finally give us the missing information necessary to unveil the production of gravitational waves during inflation, reflected by the detection of a non-zero tensor-to-scalar ratio crucial to the B-mode power spectrum of the CMB. We consider the impact of three future surveys, namely the CMB-S4, Simons Observatory, and the space-borne $\textit{LiteBIRD}$, in restricting the parameter space of four typical warm inflationary models in the context of a quartic potential, which is well motivated theoretically. We find that all three surveys significantly improve the models' parameter space, compared to recent results obtained with current $\textit{Planck}$+BICEP/Keck Array data. Moreover, the combination of ground-based and space-borne (SO+$\textit{LiteBIRD}$ and CMB-S4+$\textit{LiteBIRD}$) surveys tightens the constraints so that we expect to distinguish even better warm inflation scenarios. This result becomes clear when we compare the models' predictions with a $Λ$CDM+$r$ forecast, compatible with $r=0$, in which one of them already becomes excluded by data.

astro-ph.CO↗

arXiv2024

A comparative analysis of dissipation coefficients in warm inflation

In the warm inflation scenario, the early cosmic acceleration is driven by the inflaton coupled to thermal fields, decaying into radiation and leaving a hot universe populated by relativistic particles after the end of inflation. The interaction is usually modeled by a dissipation coefficient $Υ$ that contains the microphysics of the model. In this work, we adopt a well-motivated potential $V(ϕ)=\fracλ{4}ϕ^4$ and constrain a variety of $Υ$ parameterizations by using updated Cosmic Microwave Background data from the \textit{Planck} and \textit{BICEP/Keck Array} collaborations. We also use a Bayesian statistical criterion to compare the observational viability of these models. Our results show a significant improvement in the constraints over past results reported in the literature and also that some of these warm inflation models can be competitive compared to Starobinsky inflation.

astro-ph.CO↗

arXiv2024

Double-well Inflation: observational constraints and theoretical implications

We revisit the small field double-well inflationary model and investigate its observational viability in light of the current Cosmic Microwave Background data. In particular, considering scenarios with minimal and nonminimal coupling between the inflaton field and the Ricci scalar, we perform a Monte Carlo Markov chain analysis to probe the model's parameter space. We also investigate the consequences of the cosmological results in the canonical type-I seesaw mechanism context and obtain constraints on the vacuum expectation value of the inflaton field, together with the amplitude of the coupling to gravity in the nonminimal case. We employ a Bayesian procedure to compare the model's predictions with the Starobinsky inflationary scenario and find a strong statistical preference for the latter against the minimal and nonminimal coupled double-well scenario.

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arXiv2024

Is natural inflation in agreement with CMB data?

Natural inflation is a well-motivated model for the early universe in which an inflaton potential of the pseudo-Nambu-Goldstone form, $V(ϕ) = Λ^4[1 + \cos{(ϕ/f)}]$, can naturally drive a cosmic accelerated epoch. This paper investigates the observational viability of the minimally and non-minimally coupled natural inflation scenarios in light of current Cosmic Microwave Background (CMB) observations. We find that a small and negative coupling of the field with gravity can alleviate the well-known observational discrepancies of the minimally coupled model. We perform a Monte Carlo Markov Chain analysis of the Planck 2018 CMB and BICEP/Keck Array B-mode polarization data to estimate how strong the coupling $ξ$ should be to achieve concordance with data. We also briefly discuss the impact of these results on the physical interpretation of the natural inflation scenario.

astro-ph.CO↗

arXiv2023

Updating constraints on phantom crossing $f(T)$ gravity

We establish constraints on $f(T)$ gravity by considering the possibility of a scenario that supports a phantom crossing of the equation of state parameter $ω_{DE}$. After determining the viable parameter space of the model, while checking the impact on the background dynamics, we perform an analysis to obtain constraints on cosmological parameters and determine the viability of this scenario. To this end, we use combined data sets from cosmic chronometers (CC), baryonic acoustic oscillations (BAO), redshift space distortion (RSD) and Type Ia supernovae (SN) measurements from the latest Pantheon$+$ set, in which the impact on the absolute magnitude due to the change of the effective gravitational constant is also considered. It is found that a state where a phantom crossing of $ω_{DE}$ happens is favored by data, and the $f(T)$ model is competitive with the $Λ$CDM one by statistical criteria, such as AIC and BIC. Additionally, we find evidence of the Hubble tension being alleviated within the $f(T)$ model, at the same time that it does not worsen the growth one, indicating a possibility of the present scenario as an option to address the current cosmic tensions.

astro-ph.CO↗

arXiv2023

Constraints on the non-minimally coupled Witten-O'Raifeartaigh inflation

We investigate the impact of a non-minimal coupling of the scalar field with gravity in inflationary models, where a small coupling is allowed. As a concrete example, we consider the Witten-O'Raifeartaigh model, where, in line with other models, the presence of a coupling strength $ξ$ can recover concordance of the inflationary parameters with cosmic microwave background (CMB) constraints, provided by the Planck collaboration. We go beyond the slow-roll regime and investigate the impact in the description of CMB anisotropies by performing a statistical analysis of the model with the most recent Planck + Baryon Acoustic Oscillations (BAO) data to seek for any indication of a non-zero coupling by data within the model. We find that not only the presence of a non-minimal coupling is seen, but the model has a slight statistical preference when compared with the standard $Λ$CDM one. We also discuss the results on the minimally-coupled model, which in general, favours the simple setting where the associated mass scale is equal to the reduced Planck mass $M_p$ while being, in general, disfavored concerning the standard model.

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arXiv2022

Warm $β$-exponential inflation and the Swampland Conjectures

We investigate theoretical and observational aspects of a warm inflation scenario driven by the $β$-exponential potential, which generalizes the well-known power law inflation. In such a scenario, the decay of the inflaton field into radiation happens during the inflationary phase. In our study, we consider a dissipation coefficient ($Γ$) with cubic dependence on the temperature ($T$) and investigate the consequences in the inflationary dynamics, focusing on the impact on the spectral index $n_s$, its running $n_{run}$ and tensor-to-scalar ratio $r$. We find it possible to realize inflation in agreement with current cosmic microwave background data in weak and strong dissipation regimes. We also investigate theoretical aspects of the model in light of the swampland conjectures, as warm inflation in the strong dissipation regime has been known as a way to satisfy the three conditions currently discussed in the literature. We find that when $Γ\propto T^3$, the $β$-exponential model can be accommodated into the conjectures.

astro-ph.CO↗

arXiv2022

Revisiting Witten-O'Raifeartaigh Inflation for a Non-minimally Coupled Scalar Field

In this work, we revisit the Witten-O'Raifeartaigh model of inflation, in which the potential takes a $\operatorname{log}^2(ϕ/M)$ form, when the scalar field is non-minimally coupled to gravity. We investigate the impact of the coupling in the prediction of the inflationary parameters, thereby affecting the viability of the model. We find that a small coupling of order $ξ\sim10^{-3}$ is preferred by data at the $n_s-r$ plane level, and that the presence of a non-zero $ξ$ allows for a large interval of the mass scale $M$, in which it is possible to achieve a low tensor-to-scalar ratio. We also establish constraints imposed by a subsequent reheating era, in which its duration and temperature can be related to CMB observables, which in return, restricts the possible values for the $n_s$ and $r$ parameters.

astro-ph.CO↗

arXiv2021

Observational Constraints on $f(T)$ Gravity from Model-Independent Data

We establish new constraints on $f(T)$ gravity models by using cosmological data. In particular, we investigate the restrictions given by the gas mass fraction measurements of galaxy clusters and transversal BAO data. Both data sets are regarded as weakly dependent on a fiducial cosmology. In addition, we also include a CMB measurement of the temperature power spectrum first peak, along with $H(z)$ values from cosmic chronometers and supernovae data from the Pantheon data set. We also perform a forecast for future constraints on the deviation of $f(T)$ models from the $Λ$CDM scenario by following the specifications of the J-PAS and Euclid surveys and find significant improvements on the constraints of the $b$-parameter, when compared to the results of the statistical analysis.

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